diff --git a/infra/prism-api/src/main/java/com/evolveum/midpoint/prism/PrismNamespaceContext.java b/infra/prism-api/src/main/java/com/evolveum/midpoint/prism/PrismNamespaceContext.java
index f67ca65d8e4..093df2469da 100644
--- a/infra/prism-api/src/main/java/com/evolveum/midpoint/prism/PrismNamespaceContext.java
+++ b/infra/prism-api/src/main/java/com/evolveum/midpoint/prism/PrismNamespaceContext.java
@@ -17,10 +17,13 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Optional;
+import java.util.Random;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import com.google.common.base.Preconditions;
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableMultimap;
 import com.google.common.collect.Multimap;
@@ -337,6 +340,11 @@ private Multimap<String, String> nsToPrefix() {
             return nsToPrefix;
         }
 
+        @Override
+        public Builder childBuilder() {
+            return new Builder(this);
+        }
+
     }
 
     private static class Inherited extends PrismNamespaceContext {
@@ -415,6 +423,11 @@ public Map<String, String> allPrefixes() {
         public PrismNamespaceContext rebasedOn(PrismNamespaceContext current) {
             return parent.rebasedOn(current);
         }
+
+        @Override
+        public Builder childBuilder() {
+            return parent.childBuilder();
+        }
     }
 
     private static class Empty extends PrismNamespaceContext {
@@ -494,6 +507,11 @@ public PrismNamespaceContext rebasedOn(PrismNamespaceContext current) {
             return super.withoutDefault();
         }
 
+        @Override
+        public Builder childBuilder() {
+            return builder();
+        }
+
     }
 
     public enum PrefixPreference {
@@ -568,24 +586,99 @@ public String toString() {
 
     public static class Builder {
 
+        private PrismNamespaceContext parent;
+
         protected Builder() {
+            parent = EMPTY;
+        }
 
+        public Builder(Impl impl) {
+            parent = impl;
         }
 
         private final Map<String, String> prefixToNamespace = new HashMap<>();
+        private final Map<String, String> namespaceToPrefix = new HashMap<>();
 
         public Builder addPrefix(String prefix, String namespace) {
+            var existing = parent.namespaceFor(prefix);
+            if (existing.isPresent() && existing.get().equals(namespace)) {
+                // No need to redefine existing prefix.
+                return this;
+            }
+
+
             String previous = prefixToNamespace.putIfAbsent(prefix, namespace);
             Preconditions.checkArgument(previous == null || namespace.equals(previous), "Prefix %s is already declared as '%s', trying to redeclare it as '%s'", prefix, previous, namespace);
+            namespaceToPrefix.put(namespace, prefix);
             return this;
         }
 
         public PrismNamespaceContext build() {
-            return from(prefixToNamespace);
+            return parent.childContext(prefixToNamespace);
         }
 
         public void defaultNamespace(String defaultNamespace) {
             addPrefix(DEFAULT_PREFIX, defaultNamespace);
         }
+
+        public Optional<String> namespaceFor(String prefix) {
+            if(prefix == null) {
+                prefix = DEFAULT_PREFIX;
+            }
+            String local = prefixToNamespace.get(prefix);
+            if (local != null) {
+                return Optional.of(local);
+            }
+            return parent.namespaceFor(prefix);
+        }
+
+        public Optional<String> prefixFor(String namespace) {
+            String local = namespaceToPrefix.get(namespace);
+            if (local != null) {
+                return Optional.of(local);
+            }
+            return parent.prefixFor(namespace);
+        }
+
+        public void addPrefixes(Map<String, String> undeclaredPrefixes) {
+            for (Map.Entry<String, String> mapping : undeclaredPrefixes.entrySet()) {
+                addPrefix(mapping.getKey(), mapping.getValue());
+            }
+        }
+
+        public @NotNull String assignPrefixFor(@NotNull String namespaceURI, @Nullable String suggestedPrefix) {
+            if (Strings.isNullOrEmpty(namespaceURI)) {
+                // NO namespace, do not assign any prefix
+                return DEFAULT_PREFIX;
+            }
+            suggestedPrefix = suggestedPrefix != null ? suggestedPrefix : "gen";
+            Optional<String> directHit = namespaceFor(suggestedPrefix);
+            if (directHit.isPresent() && directHit.get().equals(namespaceURI)) {
+                // suggestedPrefix is already pointing to namespace, use it
+                return suggestedPrefix;
+            }
+
+            Optional<String> other = prefixFor(namespaceURI);
+            if (other.isPresent()) {
+                // Namespace has other prefix assigned, ignore suggested reuse parent
+                return other.get();
+            }
+
+            // We assign new prefix - suggestedPrefix or randomPrefix, if suggestedPrefix is unavailable.
+            suggestedPrefix = suggestedPrefix.isEmpty() ? "gen" : suggestedPrefix;
+            String assigned = suggestedPrefix;
+            while (namespaceFor(assigned).isPresent()) {
+                assigned = randomPrefix(suggestedPrefix);
+            }
+            addPrefix(assigned, namespaceURI);
+            return assigned;
+        }
+
+
+        private @NotNull String randomPrefix(@Nullable String base) {
+            return base + new Random().nextInt(999);
+        }
     }
+
+    public abstract Builder childBuilder();
 }
diff --git a/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/PrismQuerySerializerImpl.java b/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/PrismQuerySerializerImpl.java
index ed20a9a67ec..06aa245212e 100644
--- a/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/PrismQuerySerializerImpl.java
+++ b/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/PrismQuerySerializerImpl.java
@@ -92,8 +92,8 @@ public void emit(String prefix) {
             spaceRequired = true;
         }
 
-        public String prefixFor(String namespaceURI) {
-            return prefixes.assignPrefixFor(namespaceURI);
+        public String prefixFor(String namespaceURI, String prefix) {
+            return prefixes.assignPrefixFor(namespaceURI, prefix);
         }
 
         @Override
diff --git a/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/QueryWriter.java b/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/QueryWriter.java
index 5e3eaa57f82..7ae1fcdb113 100644
--- a/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/QueryWriter.java
+++ b/infra/prism-impl/src/main/java/com/evolveum/midpoint/prism/impl/query/lang/QueryWriter.java
@@ -17,6 +17,7 @@
 import org.jetbrains.annotations.Nullable;
 
 import com.evolveum.axiom.concepts.Builder;
+import com.evolveum.midpoint.prism.PrismNamespaceContext;
 import com.evolveum.midpoint.prism.PrismPropertyValue;
 import com.evolveum.midpoint.prism.impl.marshaller.ItemPathSerialization;
 import com.evolveum.midpoint.prism.path.ItemPath;
@@ -142,7 +143,7 @@ private Optional<String> lookupAlias(QName filter) {
 
     private void emitQName(QName filter, String additionalDefaultNs) {
         String prefix = resolvePrefix(filter, additionalDefaultNs);
-        if(prefix != null) {
+        if(!Strings.isNullOrEmpty(prefix)) {
             target.emit(prefix);
             target.emit(":");
         }
@@ -151,9 +152,9 @@ private void emitQName(QName filter, String additionalDefaultNs) {
 
     private String resolvePrefix(QName name, String additionalDefaultNs) {
         if (Strings.isNullOrEmpty(name.getNamespaceURI()) || Objects.equals(additionalDefaultNs, name.getNamespaceURI())) {
-            return null;
+            return PrismNamespaceContext.DEFAULT_PREFIX;
         }
-        return target.prefixFor(name.getNamespaceURI());
+        return target.prefixFor(name.getNamespaceURI(), name.getPrefix());
     }